@Ma**
, In that case, you can change your reason for extension from employment to being over 50 with no problem as long as you are meeting the requirements for a new reason.
You apply for cancellation at Chumchuri, then go to Chaengwattna (or the local immigration office that serves your address) to apply for a new extension before the latest stamp expires.
I think your family can also apply for the new reason as dependants to you in the same manner. But I'd like to double-check with
@T**
about your family part.